The present invention relates to an artificial lung which employs hollow fiber membranes, and more particularly to an artificial lung which includes a cylindrical housing with hollow fiber membranes disposed therein, the cylindrical housing having a blood inlet port which is displaced from the longitudinal axis of the housing so that blood introduced from the blood inlet port into the housing is swirled therein and air bubbles produced in the blood are reduced.
When a surgical operation is effected on the chest of a patient, an extracorporeal blood circulation circuit including an artificial lung, also known as an oxygenator, is used in recent years in bypassing relation to the lung of the patient, and carbon dioxide is removed from the blood of the patient and fresh oxygen is added to the blood by the artificial lung. The artificial lung in the extracorporeal blood circulation circuit employs hollow fiber membranes which can be small in size and of a rugged structure, and exchange gases stably at a high rate and are easy to handle.
One conventional artificial lung which incorporates hollow fiber membranes is shown in FIG. 1 of the accompanying drawings.
As shown in FIG. 1, the artificial lung, generally denoted at 1', comprises a cylindrical housing 4 which has a gas outlet port 15 and a gas inlet port 16, a blood outlet cover 10 mounted on the upper end of the housing 4 with a first partition 7 disposed therebetween, a blood inlet cover 9' mounted on the lower end of the housing 4 with a second partition 12 disposed therebetween, and a plurality of hollow fiber membranes 14 placed in the housing 4, for exchanging gases, the hollow fiber membranes 14 having upper ends opening into the blood outlet cover 10 and lower ends opening into the blood inlet cover 9'. The gas-exchanging hollow fiber membranes 14 extend substantially parallel to each other in the housing 4.
Each of the hollow fiber membranes 14 has a hollow space extending axially therethrough and also has a multiplicity of small holes (not shown) defined in its circumferential wall and extending radially between inner and outer wall surfaces. The hollow fiber membranes 14 may be made of a hydrophobic synthetic resin such as polypropylene. Alternatively, the hollow fiber membranes 14 may be made as porous hollow fiber membranes of a hydrophilic synthetic resin, and the inner wall surfaces thereof may be rendered hydrophobic by a silicone oil film coated thereon.
The opposite ends of the hollow fiber membranes 14 are supported in a fluid-tight fashion by the first and second partitions 7, 12, which are made of polyurethane or the like. The partitions 7, 12 divide the housing 4, the blood inlet cover 9', and the blood outlet cover 10 from each other in a fluid-tight manner, and define a gas chamber 13 therebetween within the housing 4.
Blood outlet and inlet ports 17, 26, are connected to the blood outlet and inlet cover 10, 9', respectively, and extend in the axial direction of the hollow fiber membranes 14 so that any localized flow of blood in the artificial lung 1' will be reduced. The blood outlet and inlet ports 17, 26' are joined to tubes 18a, 18b, respectively, of the extracorporeal blood circulation circuit. The hollow fiber membranes 14 of the artificial lung 1' are generally directed axially vertically so that blood will be distributed uniformly in the extracorporeal blood circulation circuit and any water which has been condensed on the outer wall surfaces of the hollow fiber membranes 14 will flow downwardly. The blood outlet port 17 is disposed at the lower end of the artificial lung 1'. Therefore, blood which flows into the blood inlet port 26' is directed upwardly, passes upwardly through the hollow fiber membranes 14 in the housing 4, and then flows out of the blood outlet port 17. The artificial lung 1' is located in the lowest position in the extracorporeal blood circulation circuit in order to prevent small air bubbles from being mixed into the blood because of air which enters the hollow fiber membranes 14, when the pressure of the blood in the extracorporeal blood circulation circuit is lowered at the time the circuit is primed or while the blood is circulating through the circuit.
However, since the blood outlet and inlet ports 17, 26' are vertically disposed and the tube 18b should not be bent sharply, the artificial lung 1' cannot be sufficiently lowered in position in the extracorporeal blood circulation circuit. The pressure of the blood in the circuit is therefore relatively low, allowing air to enter the hollow fiber membranes 14 and to be trapped as small air bubbles in the blood.
FIG. 2 of the accompanying drawings shows another known artificial lung, denoted at 1", which is designed to solve the problem of the above conventional artificial lung. The artificial lung 1" shown in FIG. 2 is disclosed in Japanese Utility Model Publication No. 61(1986)-10697. The artificial lung 1" has a blood inlet port 26' at the lower end thereof, the blood inlet port 26' being inclined at an angle ranging from 50.degree. to 100.degree. with respect to the axis of the hollow fiber membranes 14. A filter F which has a mesh size in the range of from 200 to 400 is disposed in the blood outlet cover 10 between the open ends of the hollow fiber membranes 14 and the blood outlet port 17. The artificial lung 1" can be lowered in position in the extracorporeal blood circulation circuit without the tube 18b being bent sharply. Inasmuch as the pressure of the blood in the circuit is relatively high, air is prevented from entering the hollow fiber membranes 14, and hence the danger of small air bubbles being trapped in the blood is reduced.